Description: Modus ponendo tollens 1,
one of the "indemonstrables" in Stoic logic.
See rule 1 on [Lopez-Astorga] p.
12 , rule 1 on [Sanford] p. 40, and
rule A3 in [Hitchcock] p. 5. Sanford
describes this rule second (after
mpto21540) as a "safer, and these days much more
common" version of modus
ponendo tollens because it avoids confusion between inclusive-or and
exclusive-or. (Contributed by David A. Wheeler,
3-Jul-2016.)